This invention relates generally to processing integrated circuits.
In the course of semiconductor wafer fabrication, a metal film formed on a semiconductor wafer may be polished. Conventionally, electrochemical polishing may be utilized. An abrasive fluid may be applied between the metal surface of the semiconductor wafer and a polishing platen. A potential may be applied between the semiconductor wafer and the polishing platen and the platen and semiconductor wafer may be counter rotated. As a result, the metal film may be polished.
Generally electropolish processes need uniform electrical contact to the metal film being polished. One limitation of electropolish processes is that the electrical contact to the film is made via contact to the edge of the wafer or at a few discrete points on the front of the wafer.
Thus, the electropolish process is dependent on the resistance of the film between the contact point and the area of the film being polished. As the film is thinned, the resistance of the film increases and eventually the film becomes discontinuous. As a result, the removal process is significantly slowed and may subsequently be halted in some areas.
Thus, conventional electropolish processes suffer from an inability to remove the entire metal film due to the increase in resistivity at the end of the process. Patches of metal may remain at the end of the conventional process.
Thus, there is a need for better ways to implement electrochemical polishing.